This application is based on application No. H11-023412 filed in Japan on Feb. 1, 1999, the entire content of which is hereby incorporated by reference.
The present invention relates to a compact, high-resolution display optical system that is suitable for use in an image display apparatus.
In recent years, reflection-type LCDs (liquid crystal displays) have been receiving much attention, because they allow more efficient use of light than transmission-type LCDs. Illumination light shone onto the display surface of such a reflection-type LCD is reflected therefrom pixel by pixel as projection light that has a reflection angle substantially of the same magnitude as, but of the opposite sign to, the incident angle of the illumination light (i.e. xe2x80x9cregularlyxe2x80x9d reflected). Some conventional display optical system employing a reflection-type LCD achieve image projection by shining illumination light substantially perpendicularly onto the display surface of the reflection-type LCD so that the illumination light will be reflected therefrom substantially perpendicularly as projection light and dividing the optical paths of the illumination light and the projection light by the use of a polarizing beam splitter or the like.
Some other conventional display optical systems achieve image projection by dividing the optical path into two parts, one for illumination light and the other for projection light, at the aperture-stop position.
However, in a display optical system of the former type, illumination light and projection light travel along the substantially same optical path in opposite directions. Thus, to divide the optical paths of the illumination light and the projection light, it is necessary to use a polarizing beam splitter or the like. In general, a polarizing beam splitter requires a considerably large glass block, and requires formation of multiple thin-film layers. Thus, its use leads to an undesirable increase in manufacturing cost. Moreover, irregularities within the medium of which the glass block is made disturb the polarization plane, and thereby make it impossible to inhibit the passage therethrough of unnecessary components of the light reflected from and polarized by the reflection-type LCD. This degrades the contrast of the projected image.
On the other hand, in a display optical system of the latter type, the projection optical system needs to have, in total, twice the F-numbers that is needed separately for illumination light and for projection light, and therefore needs to have an unduly large number of constituent lens elements as well as an unduly large lens diameter to offer satisfactory projection performance. This leads to an undesirable increase in manufacturing cost.
An object of the present invention is to provide a low-cost, compact, and high-resolution display optical system that is suitable for use in an image display apparatus.
To achieve the above object, according to one aspect of the present invention, a display optical system has an illumination optical system for emitting illumination light, a plurality of reflection-type display devices, a projection optical system, and a plane-parallel mirror. The reflection-type display devices individually modulate the illumination light emitted from the illumination optical system and reflect the illumination light thus modulated as projection light. The projection optical system projects the projection light and has at least one optical element included therein arranged so as to be decentered with respect to the other optical elements included therein. The plane-parallel mirror separates the illumination light into light components by reflecting a part and transmitting another part of the illumination light and then directs the light components thus separated individually to the corresponding ones of the reflection-type display devices, and integrates together the projection light reflected individually from the reflection-type display devices and then directs the projection light thus integrated together to the projection optical system.
According to another aspect of the present invention, a display optical system has an illumination optical system for emitting illumination light, a plurality of reflection-type display devices, a projection optical system for projecting projection light, and a plane-parallel mirror. The reflection-type display devices individually modulate the illumination light emitted from the illumination optical system and reflect the illumination light thus modulated as projection light. The plane-parallel mirror separates the illumination light into light components by reflecting a part and transmitting another part of the illumination light and then directs the light components thus separated individually to the corresponding ones of the reflection-type display devices, and integrates together the projection light reflected individually from the reflection-type display devices and then directs the projection light thus integrated together to the projection optical system. In this display optical system, the projection optical system has optical elements included therein arranged so as to allow separation of the optical paths of the illumination light and the projection light.
According to still another aspect of the present invention, a display optical system has an illumination optical system for emitting illumination light, a plurality of reflection-type display devices, a projection optical system for projecting projection light, and a plane-parallel mirror. The reflection-type display devices individually modulate the illumination light emitted from the illumination optical system and reflect the illumination light thus modulated as projection light. The plane-parallel mirror separates the illumination light into light components by reflecting a part and transmitting another part of the illumination light and then directs the light components thus separated individually to the corresponding ones of the reflection-type display devices, and integrates together the projection light reflected individually from the reflection-type display devices and then directs the projection light thus integrated together to the projection optical system. In this display optical system, the projection optical system has optical elements included therein arranged so as to correct the astigmatic difference caused by the plane-parallel mirror.